1. Field of the Invention
This invention pertains to a method for making dry fiber forms for use in fiber/matrix resin composites, comprised of an oriented fiber reinforcement, and a resin matrix surrounding fibers, which is subsequently cured to a "set" degree. More particularly, this invention pertains to an improvement in the manufacture of fiber forms to be employed as the reinforcing fiber structure, particularly where said fiber form is of complex design.
2. Background of the Prior Art
Increasing emphasis has been placed on the identification of materials having enhanced physical properties similar to that of various steel and metal alloys, and yet, exhibiting a significant reduction in weight for equivalent strength, and improved chemical properties, such as corrosion resistance, and the like. One field of technology that appears to offer superior promise for the identification and provision of such materials is that concerned with articles exhibiting what is generally referred to as fiber/resin matrix composite construction. Such materials are comprised of fibers, yarns, threads or similar filamentary material, often of very high modulus, which are bound together in a matrix of a curable resin, either thermosetting or thermoplastic. The resulting composite has properties superior to either component, and in advanced forms, is characterized by the fact that the fibers or yarns exhibiting a high modulus are uniformly oriented, so as to carry and transmit load in specific directions.
A number of methods have been developed for the manufacture of these fiber/resin composites. Certain systems employ fibers which are "wetted" with a resin, either uncured or preliminarily staged, which is laid down in oriented fashion, usually on a substrate of some type. In order to make complicated shapes in three dimensions, it is frequently necessary to lay down a plurality of wet layers, and subsequently trim to final, precured dimensions. These operations are variously referred to as "prepreg" or "wet lay-up" methods of manufacture.
An alternative method of manufacture, which offers enhanced flexibility, and frequently gives a product of superior performance, involves the preliminary manufacture of a fiber form, that is, an integral article comprised entirely of fibers, generally held together by a variety of secondary holding means, such as additional stitch yarns, localized glue, etc., which ultimately correspond, in general shape, to the molded article. These fiber forms are infused or otherwise saturated with resin, and subsequently cured. U.S. Pat. No. 4,681,049 discloses a method of preparing such dry fiber forms wherein the fiber form, and the ultimate part, exhibit a curve, and where orientation of the fibers is desired such that the orientation is constant along the curve.
This process, and related processes, require the initial preparation of multiple layers of the oriented structural yarns, which are subsequently cut to shape. Quite frequently, the amount of material cut away is equal to or greater than the amount of material actually needed for the ultimate part. The trimmed excess is generally waste material. Such waste represents an economical loss regardless of the nature of the fibrous or filamentary material being used. When the reinforcing fiber is of a particular and specialized type, generally selected for superior modulus and related physical characteristics, the waste can represent a severe economic drain. The cost of materials such as Kevlar.RTM. and the like, and the waste involved in preparation of composite articles incorporating those fibers, continue to help drive the cost of the overall article to a point where the article is only competitive with, and does not necessarily replace, its steel counterpart. It should be noted that, notwithstanding this fact, there is less waste involved in the dry fiber form process as described immediately above, than the prepreg or wet lay-up processes practiced as an alternative in the art.
Indeed, the waste involved in some applications renders these products questionable for certain applications. Specifically, where carbon/graphite fibers are required for their performance characteristics as the fibrous reinforcing medium, the significant amount of waste involved of what has been designated as a critical or sensitive material may preclude, or certainly render less desirable, the application of these methods, to the production of specific articles.
Accordingly, it remains a goal of the art to develop a process for the manufacture of oriented fiber/resin composites wherein the waste involved of the fiber reinforcing material is minimized. Because of the advantages derived therefrom, it would be advantageous to develop such a process in combination with the "dry" method, that is, the preparation of a dry fiber form, followed by application of a resin thereto, and curing. Such a method, however, would call for the preparation of near "net part" in fiber form production, that is, preparation of a fiber form with little or no waste.